In the field of electric arc welding there are a number of criteria upon which an electrode is evaluated by the welding industry. One of the most important criteria for an electrode is that the electrode must produce a solid, non-porous weld bead which has a tensile strength, ductility and Charpy impact value to sufficiently meet the desired end use of the welding material. With the advent of cored electrodes, including a steel sheath surrounding a core having a fluxing system and various alloying agents, there is a tremendous demand that the impact values and tensile strength be formulated to meet the requirements for a wide range of welding applications. There is a demand that the resulting weld bead have properties approaching the values obtainable in a solid wire when used in an arc welding process. Consequently, there is a tremendous demand for the formulation of a cored electrode of the type employing an external shielding gas having a desired tensile strength and an acceptable Charpy impact characteristic. Both the tensile strength and Charpy impact values are directly affected by the ultimate deposited weld metal chemistry and porosity of the weld bead after the welding process. Porosity can be caused by gases, such as nitrogen from the air, combining in the heat of the arc with the metals of the electrode as they are transferred from the electrode to the weld pool. The nitrogen components in the deposited molten metal are released as the deposited weld metal cools and solidifies. Nitrogen is normally prevented from coming into contact with the weld metal of the molten pool produced by the electric arc by including several fluxing materials, such as metal fluorides and metal oxides. These fluorides and oxides are in the core of the electrode and are released from the end of the electrode during the welding process. The electric arc and the molten metal pool in an electrode to which the present invention is directed is further shielded by flowing a continuous stream of nitrogen-free gas around the outer surface of the electrode toward the workpiece. This gas forms an envelope around the arc and prevents the nitrogen in the air from penetrating into the arc area to introduce nitrogen and oxygen into the arc and thus the molten metal formed during the welding process. The nitrogen free gas is normally argon, helium, carbon dioxide or another inert gas or mixtures thereof to shield the weld pool from nitrogen of the atmosphere. This process inhibits porosity within the weld bead as the weld bead cools.
The present invention is specifically directed to a shielded gas flux cored electrode and primarily to such an electrode having a titanium dioxide fluxing system with various oxide and certain alloying metals. The required tensile strength and Charpy impact values are normally obtained by adding various alloying ingredients to the core of the electrode, which alloys with the molten metal of the sheath to formulate a deposited weld metal bead having the desired metallurgical chemistry. The alloys which are normally incorporated in the core to form the desired alloy of the weld metal are carbon, chrome, nickel, manganese, boron, molybdenum, titanium, zirconium, and silicon. Other metals can be added in various amounts to achieve the desired Charpy impact values and tensile strength of the weld bead material. The various alloy agents or metals can be added either as elements, ferro alloys, alloys themselves, and/or oxides in combination with suitable reducing agents.
Another important criteria of welding electrodes includes the ability to weld in all positions. Different components in the core of the flux cored electrode are required to both enable the electrode to produce satisfactory weld bead profiles in both down hand, vertical and overhead positions. To produce satisfactory weld bead profiles, the flux in the core of the electrode must contain slag forming ingredients which will float to the surface of the weld bead as it cools. This slag protects the weld bead from adverse gases contained in the atmosphere which could produce pores in the weld bead during the solidification process of the material forming the weld bead. These flux ingredients are proportioned so that the solidification temperature of the mixture is below the solidification temperature of the weld bead. In this manner, the slag material on the surface of the weld bead does not adversely affect the normal shape of the surface of the weld bead as it is solidifying. In out-of-position welding, such as vertical and overhead welding, the slag formed from the material contained in the flux system of the core must not only coat the surface of the weld bead, but must also shape the profile of the bead as it solidifies. Such slag must be controlled to have sufficient viscosity so that the slag supports the molten metal of the bead in a desired position against the force of gravity during the solidification process. These two criteria of allowing the metal to solidify first and having sufficient viscosity to hold the molten metal in a desired shape when welding out of position are satisfied by known selection of the constituents in the flux system of the cored electrode. Consequently, by the proper selection of the constituents of the fluxing system a smooth weld bead having the desired profile can be created in both down hand welding and out-of-position welding.
The selection of the flux material of the electrode must also allow for easy removal of the slag after both the weld bead and flux have solidified. The various constituents to obtain the desired effect and physical characteristics of the slag created during the arc welding process are well known in the electrode technology. However, in the past, such flux cored gas shielded electrodes that contain the proper fluxing constituents and alloying agents to create the desired slag and the proper weld bead chemistry have been found to produce considerable amounts of fume, or particulate matter, which is somewhat annoying and undesirable in an arc welding process as disclosed and discussed in the various patents incorporated by reference herein.
Efforts have been made to reduce the fume created by a cored electrode used in arc welding with an external fuming gas. Fume reducing must be by a mechanism which does not destroy the ability of the electrode to perform the criteria of a weld bead having the chemistry required to attain the desired mechanical properties to produce a weld bead that is free of porosity and to produce the slag characteristics necessary for formulating the shape of the weld bead. The reduction of fume produced by such electrodes is desirable for comfort of the welder and to reduce the necessity for expensive and complicated fume exhaust systems associated with the welding process. The lower fume production of the electrode eliminates the need for expensive and bulky fume exhaust systems which are required during welding in a confined area. In addition, the welding fumes can obscure the visual observation of the weld puddle itself during the welding process. Consequently, it is desired to formulate a flux cored electrode to be used in a shielded gas welding process which maintains the desired alloying characteristics and slag characteristics with a reduction in the amount of generated fume. Prior attempts to accomplish this objective have not been successful since the prior electrodes have employed an alloying agent or reduction of carbon which only reduced a small amount of the fume created by arc welding with an external shielding gas.